Kedamono ni Lollipop

A high school girl Himari Kawashiro was unlucky to be chosen to organize a cultural festival at school. She is shy and not very popular with her classmates, so she is really troubled by the task. Accidentally she finds a cat eating sweets in an empty room. She takes it and suddenly the cat turns into her classmate Sennojou Shionji. He is rich, extremely good-looking and popular, but also a very arrogant boy. He explains Himori that he is a half-beast and needs sugar to maintain his human form, though he hates sweets. He demands Himori to keep it secret. In return she asks him to help her with the cultural festival. He agrees on condition that she becomes his servant at school. Thus, the story of Himari and sweets hating half-beast Shionji begins...

(Source: Raffmanga)